Which South African plants are best for warding off mosquitos? That’s the question raised by a team of researchers from the Durban University of Technology, in a paper published in the journal Tropical Medicine. The team set about looking for locally sourced, natural ‘eco-friendly’ alternatives to synthetic repellents, and found at least one which is as effective as N,N-Diethyl-3-methylbenzamide, aka DEET.
According to the paper, The antimosquito properties of extracts from flowering plants in South Africa, there are major concerns about the long-term usefulness of synthetic repellents and insecticides as the insects themselves develop immunities over time. ‘Natural’ plant-based alternatives, especially of South African plants, haven’t been well studied, however, and knowledge is dying away.
“Information on these (African) medicinal plants is dominated by oral tradition and is not always scientifically well documented,” write the authors. “This traditional information is further complicated by loss of biodiversity and tradition and there is a clear need for accurate documentation of knowledge of traditional herbalists.”
Of all the planet’s creatures, the humble mosquito is – in my opinion – the most malevolent. The International Red Cross says that more people are killed by the disease spreading insect than any other animal, including almost a million people who die of malaria, and scientists appear to be more or less in accord when they say that the only side effect of eradicating the bug would be fewer humans getting sick. For myself, the tiny mosquito has been one of the very few unpleasant parts of the experience of moving to South Africa – itchy sleepless nights and infected scratch wounds are definitely something I wouldn’t miss if I ever moved back to the UK.
DEET, the synthetic chemical used in almost all current mosquito repellents, is highly effective at deterring the biters, but it has to be regularly applied, smells foul and is quite pricey. It also comes with a terrifying list of contraindications ranging from nausea to reports of encephalitis in children who are doused in it. They’re not as bad as full blown malaria, of course, but neither are they something you really look forward to of a summer evening.
Which makes it all the more surprising that some of the plant-based repellents mentioned in oral or traditional medicines haven’t been more thoroughly tested yet.
The Durban team, led by Prof Bharti Odhav, tested 24 samples from 12 South African plants and while they found none had significant insecticidal properties for killing off mosquitoes, Leonotis leonurus – aka Lions Tail or Wild Dagga – was as effective as DEET in keeping the little blighters away. L leonurus is used widely in traditional medicines, but is apparently also known for its similarity to cannabis when smoked.
Wild Dagga is most effective when prepared in a methanolic compound, apparently. The team also found that pink guava, Strawberry Guava and Ashanti pepper were equally effective when prepared in the same way.
The paper recommends further research to establish which compounds in the most promising plants have the repellent properties, but speculates that it’s likely to be concentrations of tannins, malic acid and citric acid. The next stage of research will involve field trials.
(Main image – cc Alvesgaspar)